Method and apparatus for writing data on storage medium

ABSTRACT

A data recording method according to the present invention is a method for recording data as edge position information, including marks and spaces of multiple different lengths, on a storage medium by irradiating the storage medium with a pulsed energy beam. The method includes the steps of: (A) generating a write code sequence based on the data to be recorded; (B) determining a write pulse waveform, defining the power modulation of the energy beam, according to the code lengths of respective codes included in the write code sequence; and (C) modulating the power of the energy beam based on the write pulse waveform. If the shortest code length of the write code sequence is n (which is an integer equal to or greater than one), a write pulse waveform that has only one write pulse is assigned to recording mark making periods corresponding to codes with code lengths x of n, n+1 and n+2, and a write pulse waveform that has multiple write pulses Pw is assigned to recording mark making periods corresponding to codes with code lengths x of n+3 or more.

This application is a continuation application of U.S. patentapplication Ser. No. 12/133,619 filed on Jun. 5, 2008 which is acontinuation of U.S. application Ser. No. 10/551,573 filed on Oct. 3,2005, which is a §371 of International Application No. PCT/JP2004/004224filed Mar. 25, 2004, the entire disclosures of which are incorporatedherein by reference, and is related to sibling U.S. application Ser.Nos. 12/133,651 and 12/133,666 both filed on Jun. 5, 2008 and U.S.application Ser. No. 12/180,681 filed on Jul. 28, 2008.

TECHNICAL FIELD

The present invention relates to a method and apparatus for recordingdata (or information) on a storage medium such as an optical disk byirradiating the storage medium with a laser beam or any other energybeam so as to make a mark having a different physical property from anon-recorded portion thereof.

BACKGROUND ART

A rewritable optical disk such as a DVD-RAM has a phase change recordinglayer on its substrate. When this phase change recording layer isirradiated with a laser beam having a high energy density, theirradiated portion is locally heated to a temperature exceeding themelting point and melted. Since the optical disk being irradiated withthe laser beam is spinning at a high velocity, the beam spot of thelaser beam will be moving along the track on the phase change recordinglayer at a high velocity, too. That is why that portion of the phasechange recording layer that has been melted by the passage of the beamspot is quickly cooled and solidified naturally. If the power of thelaser beam is adjusted in such a situation, then the melted portion ofthe phase change recording layer is rapidly cooled and amorphized. Theamorphized portion of the phase change recording layer has a differentrefractive index and a different optical reflectance from those of theother crystalline portions. The amorphized portion formed in this manneris called a “mark”. On the other hand, an intervening portion betweenthose “marks” on the track is called a “space”.

By arranging those marks and spaces on the track, data can be recordedon the optical disk. If a laser beam with a low power for reading isradiated toward the optical disk and if the intensity of its reflectedlight is measured, then the mark/space boundary (which is often called a“mark edge”) can be sensed and data can be read. The power of the readlaser beam is kept low enough to avoid melting the phase changerecording layer.

To increase the information transfer rate while data is being read from,or written on, any of those optical disks, either the recording lineardensity or the scanning rate of the beam spot on the optical disk may beincreased.

In order to increase the recording linear density, it is effective toreduce the mark length and space length or to narrow the mark edgeposition detecting interval by reducing the steps of variations in markand space lengths.

However, if the recording linear density were increased, then the SNR ofthe read signal would decrease. For that reason, a significant increasein recording linear density should not be expected.

To make very small marks on an optical disk with high precision, a writestrategy, in which each of those marks is left on the recording layer bycontinuously irradiating that layer with either a single laser pulse ormultiple laser pulses, is adopted.

According to a conventional technique as disclosed in Japanese PatentApplication Laid-Open Publication No. 5-298737 (which will be referredto herein as a “first conventional technique”), a train of laser pulsesis assigned to each of multiple marks with different lengths. In otherwords, a train of laser pulses to be radiated to make each mark, i.e., awaveform showing the intensity variation of the laser beam (which willbe referred to herein as a “write pulse waveform”), is determined by thelength of that mark to leave. The number and amplitude of pulses to beradiated during the period of making each mark are controlled accordingto the length of a write code sequence.

The write pulse waveform during the mark making period can be dividedinto a top portion and a succeeding portion. The respective pulsesgenerally have different pulse heights. Also, in the periods other thanthe mark making period, a write auxiliary pulse is generated to followthe space.

According to the technique disclosed in Japanese Patent ApplicationLaid-Open Publication No. 5-298737, the diffusion of heat from apreceding mark toward the front edge of the very next mark can becompensated for, and the mark width and mark edge position can becontrolled with high precision, irrespective of the space length.

According to another conventional technique as disclosed in JapanesePatent Application Laid-Open Publication No. 8-7277 (which will bereferred to herein as a “second conventional technique”), each writecode is broken down into a plurality of primitive elements with multipledifferent lengths such that a single write pulse is associated with eachof those elements. And each write code is formed by a series ofrecording marks associated with respectively independent write pulses.

Still another conventional technique as disclosed in Japanese PatentApplication Laid-Open Publication No. 9-134525 (which will be referredto herein as a “third conventional technique”) adopts a multi-pulsewriting method that uses the first heating pulse, a number of succeedingheating and cooling pulses that follow the first pulse, and the lastcooling pulse. According to the third conventional technique, inrecording a mark, of which the length is either an odd number of timesor an even number of times as long as one period of a write channelclock, the pulse width of the succeeding heating and cooling pulses ismade nearly equal to the length of one period of the write channelclock.

According to yet another conventional technique as disclosed in JapanesePatent Application Laid-Open Publication No. 11-175976 (which will bereferred to herein as a “fourth conventional technique”), the energy andthe number of pulses that are applied while a mark of an arbitrarylength is being made are changed according to the length of the mark ina write code sequence such that the gap between two arbitrary variationpoints of the energy applied per unit time during the mark making periodbecomes longer than a half of the detection window width.

According to the first conventional technique, the length of a mark,corresponding with the detection window width, is associated with oneshot of write pulse. Thus, if the detection window width is shortened,then the semiconductor laser diode, functioning as a source ofgenerating write energy, needs to be driven faster than usual. Forexample, if one tries to realize a burst transfer rate of 10 megabytesper second, which is almost as high as that of a magnetic disk drive, bya normal (1, 7) modulation technique, then the detection window width ofthe read signal will be about 8.3 ns (nanoseconds) and therefore theshortest write current pulse width will be about 4.2 ns, which isapproximately a half as long as the detection window width. However, itusually takes several nanoseconds to activate a semiconductor laser, andit is difficult to generate a write beam pulse accurately. Also, even ifa write beam pulse could be generated accurately, normal marks could notbe made in a situation where multi-pulse writing is carried out on amedium such as a phase change disk in which the mark making iscontrolled by the cooling rate of its heated portion. This is becausethe next beam pulse is radiated before the heated portion is cooledsufficiently. Also, if one tries to realize a burst transfer rate of 10megabytes per second by the (1, 7) modulation technique, for example,then the amount of time it takes to cool the storage medium will also beabout 4.2 ns, which is equal to the shortest write current pulse width.Consequently, marks could not be made properly depending on the propertyof the storage medium.

According to the second conventional technique mentioned above, eachwrite code is broken down into a plurality of primitive elements withmultiple different lengths such that a single write pulse is associatedwith each of those elements and that each write code is formed by aseries of recording marks associated with respectively independent writepulses. However, this conventional technique does not consider thermalbalance between write pulses for respective elements at all. That is whyas the recording linear density is increased, it becomes more and moredifficult to control the mark edge position. That is to say, in makingmarks that will form a single write code, the recording marks will havevariable widths from one position to another because the quantity ofheat accumulated in the recording layer for the top portion of the writecode is different from that of heat accumulated there for the terminalportion of the write code. As a result, the edge recording cannot becarried out as intended.

In the third conventional technique, a pulse, which is much shorter thanthe detection window width, may be inserted into the write pulsewaveform in the vicinity of the center of the mark making period, andthe mark width changes significantly around there compared to the otherportions. According to the document disclosing this conventionaltechnique, when a mark edge recording operation is carried out, thevariation in signal amplitude around the center portion of a mark shouldcause no serious problem as long as the mark edge position is accurate.In a read/write drive that determines read/write conditions by detectingthe average level of a read signal, however, such distortion of the readsignal should affect the operation of the drive. As to a phase changestorage medium, for example, a signal can be detected as a variation inreflectance just like a phase pit type storage medium. That is why thephase change storage medium and phase pit type storage medium can easilyshare the same read drive in common. However, since the read signal ofthe phase pit type storage medium has no such distortion, it is actuallydifficult to read the phase change storage medium and phase pit typestorage medium using the same drive.

Also, according to the fourth conventional technique, the write powerlevel of the write pulse train changes stepwise, thus requiringcomplicated power control. Also, in writing a signal with a code lengthof 4 Tw, the laser beam needs to be emitted so as to achieve a higherpower level than the average power level at least for a period of timecorresponding to 3 Tw. When a very small mark needs to be made on ahigh-density storage medium in the near future, such an emission timewill be too long to make desired recording marks.

As can be seen, none of the conventional techniques mentioned above cancontribute to making marks sufficiently accurately when the transferrate is high or achieving sufficiently high storage plane density andreliability.

In order to overcome the problems described above, an object of thepresent invention is to provide a method and apparatus for recordingdata that can make marks with high accuracy even when the transfer rateis high.

DISCLOSURE OF INVENTION

A data recording method according to the present invention is a methodfor recording data as edge position information, including marks andspaces of multiple different lengths, on a storage medium by irradiatingthe storage medium with a pulsed energy beam. The method includes thesteps of: (A) generating a write code sequence based on the data to berecorded; (B) determining a write pulse waveform, defining the powermodulation of the energy beam, according to the code lengths ofrespective codes included in the write code sequence; and (C) modulatingthe power of the energy beam based on the write pulse waveform. If theshortest code length of the write code sequence is n (which is aninteger equal to or greater than one), the step (B) includes assigning awrite pulse waveform that has only one write pulse to recording markmaking periods corresponding to codes with code lengths x of n, n+1 andn+2, and a write pulse waveform that has multiple write pulses Pw torecording mark making periods corresponding to codes with code lengths xof n+3 or more, respectively.

In one preferred embodiment, if the shortest code length of the writecode sequence is n (which is an integer equal to or greater than one),the step (B) includes classifying the code lengths x into at least fourlengths including n, n+1, n+2 and n+3 or more. As to two codes, whichhave code lengths m and m+1, respectively, and which have the samenumber of write pulses Pw in the recording mark making period of theirwrite pulse waveforms, the step (B) includes determining the write pulsewaveforms so as to satisfy the inequality: (write pulse width of codelength m)≦(write pulse width of code length m+1), where the “write pulsewidth of code length m” is the width of an arbitrary Kth write pulseperiod included in the recording mark making period corresponding to thecode length m and the “write pulse width of code length m+1” is thewidth of the Kth write pulse period included in the recording markmaking period corresponding to the code length m+1.

In another preferred embodiment, as to two codes, which have codelengths m and m+1, respectively, and which have the same number of writepulses Pw and the same number of periods with a bottom power level Pbbetween two write pulses Pw in the recording mark making period of theirwrite pulse waveforms, the step (B) includes determining the write pulsewaveforms so as to satisfy the inequality: (pulse width of code lengthm)≦(pulse width of code length m+1), where the “pulse width of codelength m” is the width of an arbitrary Kth period with the bottom powerlevel Pb included in the recording mark making period corresponding tothe code length m and the “pulse width of code length m+1” is the widthof the Kth period with the bottom power level Pb included in therecording mark making period corresponding to the code length m+1.

In another preferred embodiment, the write pulse waveform in therecording mark making period corresponding to codes with code lengths xof n+3 or more includes write pulses, of which the number is equal tothe quotient obtained by dividing (x−1) by two.

In another preferred embodiment, in the recording mark making periodcorresponding to codes with code lengths x of n+3 or more, the length ofa period in which the write pulse waveform has an erasure power level Peis set to be at least equal to 1 Tw.

In another preferred embodiment, in each said recording mark makingperiod, the length of a period in which the write pulse waveform has thebottom power level Pb is set to be at least equal to 1 Tw.

In another preferred embodiment, in each said recording mark makingperiod, the length of a period in which the write pulse waveform has acooling power level Pc is set to be at least equal to 1 Tw.

In another preferred embodiment, the start position of the first pulse,included in a recording mark making period of the write pulse waveform,and the end position of a cooling pulse, also included in the recordingmark making period, are shifted according to the length x of a codeassociated with the recording mark making period.

In another preferred embodiment, the positions are shifted to at leastfour different degrees corresponding to the code lengths x of n, n+1,n+2 and n+3 or more.

An apparatus according to the present invention is an apparatus forrecording data as edge position information, including marks and spacesof multiple different lengths, on a storage medium by irradiating thestorage medium with a pulsed energy beam. The apparatus includes: laserdriving means for modulating the power of the energy beam; coding meansfor converting the data to be recorded on the storage medium into awrite code sequence; and mark length classifying means for determining awrite pulse waveform, defining the power modulation of the energy beam,according to the code lengths x of respective codes included in thewrite code sequence. If the shortest code length of the write codesequence is n (which is an integer equal to or greater than one), themark length classifying means assigns a write pulse waveform that hasonly one write pulse Pw to recording mark making periods correspondingto codes with code lengths x of n, n+1 and n+2, and a write pulsewaveform that has multiple write pulses Pw to recording mark makingperiods corresponding to codes with code lengths x of n+3 or more,respectively.

In one preferred embodiment, as to two codes, which have code lengths mand m+1, respectively, and which have the same number of write pulses Pwand the same number of periods with a bottom power level Pb between twowrite pulses Pw in the recording mark making period of their write pulsewaveforms, the write pulse waveforms are determined so as to satisfy theinequality: (pulse width of code length m)≦(pulse width of code lengthm+1), where the “pulse width of code length m” is an arbitrary Kthperiod with the bottom power level included in the recording mark makingperiod corresponding to the code length m and the “pulse width of codelength m+1” is the Kth period with the bottom power level included inthe recording mark making period corresponding to the code length m+1.

In another preferred embodiment, if the shortest code length of thewrite code sequence is n (which is an integer equal to or greater thanone), the code lengths x are classified into at least four lengthsincluding n, n+1, n+2 and n+3 or more. As to two codes, which have codelengths m and m+1, respectively, and which have the same number of writepulses Pw in the recording mark making period of their write pulsewaveforms, the write pulse waveforms are determined so as to satisfy theinequality: (write pulse width of code length m)≦(write pulse width ofcode length m+1), where the “write pulse width of code length m” is thewidth of an arbitrary Kth write pulse period included in the recordingmark making period corresponding to the code length m and the “writepulse width of code length m+1” is the width of the Kth write pulseperiod included in the recording mark making period corresponding to thecode length m+1.

In another preferred embodiment, as to two codes, which have codelengths m and m+1, respectively, and which have the same number of writepulses Pw and the same number of periods with a bottom power level Pbbetween two write pulses Pw in the recording mark making period of theirwrite pulse waveforms, the write pulse waveforms are determined so as tosatisfy the inequality: (pulse width of code length m)≦(pulse width ofcode length m+1), where the “pulse width of code length m” is the widthof an arbitrary Kth period with the bottom power level Pb included inthe recording mark making period corresponding to the code length m andthe “pulse width of code length m+1” is the width of the Kth period withthe bottom power level Pb included in the recording mark making periodcorresponding to the code length m+1.

In another preferred embodiment, the write pulse waveform in therecording mark making periods corresponding to codes with code lengths xof n+3 or more is determined so as to include a number of write pulsesthat is equal to the quotient obtained by dividing (x−1) by two.

In another preferred embodiment, the write pulse waveforms aredetermined such that every interval between trailing and leading edgesof a fundamental waveform of a laser pulse in the mark making periodsbecomes at least equal to a detection window width Tw.

In another preferred embodiment, the apparatus includes pulse shiftingmeans for shifting the start position of the first pulse, included in arecording mark making period of the write pulse waveform, and the endposition of a cooling pulse, also included in the write pulse waveform,according to the length x of a code associated with the recording markmaking period.

In another preferred embodiment, the apparatus includes writecompensating means for shifting the positions to at least four differentdegrees corresponding to the code lengths x of n, n+1, n+2 and n+3 ormore.

Another data recording method according to the present invention is amethod for recording data as edge position information, including marksand spaces of multiple different lengths, on a storage medium byirradiating the storage medium with a pulsed energy beam. The methodincludes the steps of: (A) generating a write code sequence based on thedata to be recorded; (B) determining a write pulse waveform, definingthe power modulation of the energy beam, according to the code lengthsof respective codes included in the write code sequence; and (C)modulating the power of the energy beam based on the write pulsewaveform. The step (B) includes setting the number of write pulses Pw,included in respective recording mark making periods of the write pulsewaveforms corresponding to code lengths n and n+1, to be equal to one,and making the width of the write pulse Pw, included in the recordingmark making period of the write pulse waveform corresponding to the codelength n, equal to or smaller than that of the write pulse Pw includedin the recording mark making period of the write pulse waveformcorresponding to the code length n+1. The step (B) also includes settingthe number of write pulses Pw, included in respective recording markmaking periods of the write pulse waveforms corresponding to codelengths n+2 and n+3, to be equal to two, and making the width of a firstwrite pulse Pw, included in the recording mark making period of thewrite pulse waveform corresponding to the code length n+2, equal to orsmaller than that of a first write pulse Pw included in the recordingmark making period of the write pulse waveform corresponding to the codelength n+3. And the step (B) further includes making the width of asecond write pulse Pw, included in the recording mark making period ofthe write pulse waveform corresponding to a code length n+2, equal to orsmaller than that of a second write pulse Pw included in the recordingmark making period of the write pulse waveform corresponding to a codelength n+3.

Still another data recording method according to the present inventionis a method for recording data as edge position information, includingmarks and spaces of multiple different lengths, on a storage medium byirradiating the storage medium with a pulsed energy beam. The methodincludes the steps of: (A) generating a write code sequence based on thedata to be recorded; (B) determining a write pulse waveform, definingthe power modulation of the energy beam, according to the code lengthsof respective codes included in the write code sequence; and (C)modulating the power of the energy beam based on the write pulsewaveform. If the shortest code length of the write code sequence is n(which is an integer equal to or greater than one), the step (B)includes classifying the code lengths x into at least four lengthsincluding n, n+1, n+2 and n+3 or more. As to two codes, which have codelengths m and m+1, respectively, and which have the same number of writepulses Pw in the recording mark making period of their write pulsewaveforms, the step (B) includes determining the write pulse waveformsso as to satisfy the inequality: (write pulse width of code lengthm)≦(write pulse width of code length m+1), where the “write pulse widthof code length m” is the width of an arbitrary Kth write pulse periodincluded in the recording mark making period corresponding to the codelength m and the “write pulse width of code length m+1” is the width ofthe Kth write pulse period included in the recording mark making periodcorresponding to the code length m+1.

Yet another data recording method according to the present invention isa method for recording data as edge position information, includingmarks and spaces of multiple different lengths, on a storage medium byirradiating the storage medium with a pulsed energy beam. The methodincludes the steps of: (A) generating a write code sequence based on thedata to be recorded; (B) determining a write pulse waveform, definingthe power modulation of the energy beam, according to the code lengthsof respective codes included in the write code sequence; and (C)modulating the power of the energy beam based on the write pulsewaveform. As to two codes, which have code lengths m and m+1,respectively, and which have the same number of write pulses Pw and thesame number of periods with a bottom power level Pb between two writepulses Pw in the recording mark making period of their write pulsewaveforms, the step (B) includes determining the write pulse waveformsso as to satisfy the inequality: (pulse width of code length m)≦(pulsewidth of code length m+1), where the “pulse width of code length m” isthe width of an arbitrary Kth period with the bottom power level Pbincluded in the recording mark making period corresponding to the codelength m and the “pulse width of code length m+1” is the width of theKth period with the bottom power level Pb included in the recording markmaking period corresponding to the code length m+1.

Another apparatus according to the present invention is an apparatus forrecording data as edge position information, including marks and spacesof multiple different lengths, on a storage medium by irradiating thestorage medium with a pulsed energy beam. The apparatus includes: laserdriving means for modulating the power of the energy beam; coding meansfor converting the data to be recorded on the storage medium into awrite code sequence; and mark length classifying means for determining awrite pulse waveform, defining the power modulation of the energy beam,according to the code lengths x of respective codes included in thewrite code sequence. The mark length classifying means sets the numberof write pulses Pw, included in respective recording mark making periodsof the write pulse waveforms corresponding to code lengths n and n+1, tobe equal to one, and makes the width of the write pulse Pw, included inthe recording mark making period of the write pulse waveformcorresponding to the code length n, equal to or smaller than that of thewrite pulse Pw included in the recording mark making period of the writepulse waveform corresponding to the code length n+1. The mark lengthclassifying means also sets the number of write pulses Pw, included inrespective recording mark making periods of the write pulse waveformscorresponding to code lengths n+2 and n+3, to be equal to two, and makesthe width of a first write pulse Pw, included in the recording markmaking period of the write pulse waveform corresponding to the codelength n+2, equal to or smaller than that of a first write pulse Pwincluded in the recording mark making period of the write pulse waveformcorresponding to the code length n+3. And the mark length classifyingmeans further makes the width of a second write pulse Pw, included inthe recording mark making period of the write pulse waveformcorresponding to a code length n+2, equal to or smaller than that of asecond write pulse Pw included in the recording mark making period ofthe write pulse waveform corresponding to a code length n+3.

Still another apparatus according to the present invention is anapparatus for recording data as edge position information, includingmarks and spaces of multiple different lengths, on a storage medium byirradiating the storage medium with a pulsed energy beam. The apparatusincludes: laser driving means for modulating the power of the energybeam; coding means for converting the data to be recorded on the storagemedium into a write code sequence; and mark length classifying means fordetermining a write pulse waveform, defining the power modulation of theenergy beam, according to the code lengths x of respective codesincluded in the write code sequence. If the shortest code length of thewrite code sequence is n (which is an integer equal to or greater thanone), the mark length classifying means classifies the code lengths xinto at least four lengths including n, n+1, n+2 and n+3 or more. As totwo codes, which have code lengths m and m+1, respectively, and whichhave the same number of write pulses Pw in the recording mark makingperiod of their write pulse waveforms, the mark length classifying meansdetermines the write pulse waveforms so as to satisfy the inequality:(write pulse width of code length m)≦(write pulse width of code lengthm+1), where the “write pulse width of code length m” is the width of anarbitrary Kth write pulse period included in the recording mark makingperiod corresponding to the code length m and the “write pulse width ofcode length m+1” is the width of the Kth write pulse period included inthe recording mark making period corresponding to the code length m+1.

Yet another apparatus according to the present invention is an apparatusfor recording data as edge position information, including marks andspaces of multiple different lengths, on a storage medium by irradiatingthe storage medium with a pulsed energy beam. The apparatus includes:laser driving means for modulating the power of the energy beam; codingmeans for converting the data to be recorded on the storage medium intoa write code sequence; and mark length classifying means for determininga write pulse waveform, defining the power modulation of the energybeam, according to the code lengths x of respective codes included inthe write code sequence. As to two codes, which have code lengths m andm+1, respectively, and which have the same number of write pulses Pw andthe same number of periods with a bottom power level Pb between twowrite pulses Pw in the recording mark making period of their write pulsewaveforms, the mark length classifying means determines the write pulsewaveforms so as to satisfy the inequality: (pulse width of code lengthm)≦(pulse width of code length m+1), where the “pulse width of codelength m” is the width of an arbitrary Kth period with the bottom powerlevel Pb included in the recording mark making period corresponding tothe code length m and the “pulse width of code length m+1” is the widthof the Kth period with the bottom power level Pb included in therecording mark making period corresponding to the code length m+1.

Yet another data recording method according to the present invention isa method for recording data as edge position information, includingmarks and spaces of multiple different lengths, on a storage medium byirradiating the storage medium with a pulsed energy beam. The methodincludes the steps of: (A) generating a write code sequence based on thedata to be recorded; (B) determining a write pulse waveform, definingthe power modulation of the energy beam, according to the code lengthsof respective codes included in the write code sequence; and (C)modulating the power of the energy beam based on the write pulsewaveform. As to two codes, which have code lengths m and m+1,respectively, and which have the same number of write pulses Pw in therecording mark making period of their write pulse waveforms, the writepulse waveforms are determined so as to satisfy the inequality: (writepulse width of code length m)≦(write pulse width of code length m+1),where the “write pulse width of code length m” is the width of anarbitrary Kth write pulse period included in the recording mark makingperiod corresponding to the code length m and the “write pulse width ofcode length m+1” is the width of the Kth write pulse period included inthe recording mark making period corresponding to the code length m+1.

Yet another data recording method according to the present invention isa method for recording data as edge position information, includingmarks and spaces of multiple different lengths, on a storage medium byirradiating the storage medium with a pulsed energy beam. The methodincludes the steps of: (A) generating a write code sequence based on thedata to be recorded; (B) determining a write pulse waveform, definingthe power modulation of the energy beam, according to the code lengthsof respective codes included in the write code sequence; and (C)modulating the power of the energy beam based on the write pulsewaveform. As to two codes, which have code lengths m and m+1,respectively, and which have the same number of write pulses Pw and thesame number of periods with a bottom power level Pb between two writepulses Pw in the recording mark making period of their write pulsewaveforms, the write pulse waveforms are determined so as to satisfy theinequality: (pulse width of code length m)≦(pulse width of code lengthm+1), where the “pulse width of code length m” is the width of anarbitrary Kth period with the bottom power level Pb included in therecording mark making period corresponding to the code length m and the“pulse width of code length m+1” is the width of the Kth period with thebottom power level Pb included in the recording mark making periodcorresponding to the code length m+1.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 shows an overall configuration for an apparatus according to thepresent invention.

FIG. 2 shows a configuration for the recording processing system shownin FIG. 1.

Portions (a) through (h) of FIG. 3 show how the recording processingsystem works in the present invention and in the prior art.

Portions (a) through (j) of FIG. 4 show write pulse waveforms adopted ina first preferred embodiment of an apparatus according to the presentinvention.

Portions (a) through (i) of FIG. 5 show write pulse waveforms for therecording processing system of a conventional data recorder (as acomparative example).

Portions (a) through (j) of FIG. 6 show write pulse waveforms adopted ina second preferred embodiment of an apparatus according to the presentinvention.

Portions (a) through (j) of FIG. 7 show write pulse waveforms adopted ina third preferred embodiment of an apparatus according to the presentinvention.

FIG. 8 shows how adaptive mark compensation can be done according to thepresent invention.

FIG. 9 shows how adaptive mark compensation can be done according to thepresent invention.

FIG. 10 shows a configuration for the recording processing system of aconventional data recorder.

Portions (a) through (j) of FIG. 11 show write pulse waveforms adoptedin a fourth preferred embodiment of an apparatus according to thepresent invention.

Portions (a) through (j) of FIG. 12 show write pulse waveforms adoptedin a fifth preferred embodiment of an apparatus according to the presentinvention.

FIGS. 13( a) and 13(b) show two types of write pulse waveforms formaking a 4 Tw mark, and FIGS. 13( c) and 13(d) schematically illustratethe shapes of marks left.

BEST MODE FOR CARRYING OUT THE INVENTION

In a conventional write strategy for optical disk drives, the number ofpulses for multi-pulse writing is increased such that the resultant markwill not have an expanded end portion.

The present inventors discovered that when data needed to be recorded ata high rate, the mark shape could be kept appropriate by increasing thepulse width, not the number of pulses for multi-pulse writing, thusacquiring the basic idea of the present invention. Suppose the datatransfer rate will go beyond 72 Mbps in the near future. In that case,according to the conventional write strategy that uses a lot of pulsesfor multi-pulse writing, a semiconductor laser, functioning as a lightsource in a drive for recording data, will need to have a furtherincreased operating frequency. Actually, however, it is difficult tofurther increase the operating frequency of semiconductor lasers.

In contrast, in a preferred embodiment of the present invention, data isrecorded with just one pulse applied in making relatively short markswith code lengths of 2 Tw to 4 Tw as will be described later, and thereis no need to further improve the performance of semiconductor lasers.In addition, since resultant marks have appropriate shapes, read errorsnever increase, either.

Hereinafter, preferred embodiments of the present invention will bedescribed with reference to the accompanying drawings.

Embodiment 1

A first preferred embodiment of a data recorder according to the presentinvention will be described.

In this preferred embodiment, a phase change optical disk is used as astorage medium. However, the storage media that may be used in thepresent invention are not limited to optical disks of that type. Anyother type of storage medium can also be used effectively in the presentinvention as long as the storage medium can locally make a “mark” with adifferent physical property from the other portions by applying somenon-optical energy such as magnetic energy or electron beam to thestorage medium.

The present invention is characterized by its write strategy ofcontrolling the level of energy applied to a storage medium in recordingdata on the storage medium (i.e., write energy) highly precisely. Asused herein, the “write energy level” means the average energy level ofa laser beam in a period of time that is approximately a half as long asthe detection window width (which is a unit of variation in the edgeposition of marks and spaces). If a frequency component that is muchhigher than the frequency of a period corresponding to the detectionwindow width is superposed on a write pulse waveform for some reason(e.g., to minimize laser noise), then the “write energy level” means anaverage energy level of a period of time that is long enough to neglectthe influence of that frequency component.

First, referring to FIG. 1, illustrated is an overall configuration fora data recorder according to a preferred embodiment of the presentinvention. As shown in FIG. 1, the apparatus of this preferredembodiment includes an optical pickup, a write processing system and aread processing system.

The optical pickup includes a laser 110 for radiating a laser beam 123,a collimator lens 109 for transforming the laser beam 123 into parallellight, a half mirror 108, an objective lens 116 for condensing the laserbeam 123 onto an optical disk 117, a detector lens 106 for condensingthe light that has been reflected from the optical disk 117, aphotodetector 100 for detecting the reflected light, and a pre-amplifier101 for amplifying the output of the photodetector 100.

In this preferred embodiment, the laser 110 may be a semiconductor laserthat oscillates at a wavelength of 405 nm and the objective lens 116 mayhave an NA of 0.85, for example. Only one laser 110 and its accompanyingoptical system are shown in FIG. 1. However, the single optical pickupmay include a light source module for emitting laser beams with multipledifferent wavelengths and their associated optical systems.

The write processing system shown in FIG. 1 includes a data modulator113 for converting write data 127 into a write code sequence (NRZI) 126,a write pulse waveform generator 112 for generating a level producingsignal 125 based on the write code sequence (NRZI) 126, a pulse shifter115 for generating a pulse generation signal 130 based on the levelproducing signal 125, and a laser driver 111 for outputting laser drivecurrent 124 responsive to the pulse generation signal 130. A referenceclock signal 128 is supplied from a reference clock generator 119 to thedata modulator 113 and write pulse waveform generator 112. In thispreferred embodiment, the reference clock signal 128 has a frequency of72 MHz and a detection window width Tw of 7.58 ns. The write processingsystem further includes a power setter 114 and a write compensator 118.

The read processing system shown in FIG. 1 includes a equalizer 103 thatreceives the read signal 120 as the output signal of the pre-amplifier101 of the optical pickup and subjects the signal to waveform equalizingprocess, a digitizer 104 for converting the read signal into a digitalread signal 121, and a decoder 105 for generating read data 122 bydecoding the digital read signal 121.

Next, it will be described how the data recorder shown in FIG. 1operates.

The data modulator 113 of the write processing system receives the writedata 127 to be written on the optical disk 117 and converts this writedata 127 into the write code sequence (NRZI) 126 representing the marksand spaces to be made on the optical disk 117. The write wave generator112 receives the write code sequence 126 and converts it into the levelproducing signal 125 corresponding to the write pulse waveform. The datamodulator 113 and write pulse waveform generator 112 operate in responseto the reference clock signal 128 generated by the reference clockgenerator 119.

The pulse shifter 115 receives the level producing signal 125 andforwards it as the pulse generation signal 130 to the laser driver 111.In this case, the pulse shifter 115 compensates for the pulsed waveformof the level generating signal 125 on the time axis in accordance with awrite compensation table value of the write compensator 118, therebymaking the pulse generation signal 130.

The laser driver 111 generates the laser drive current 124 responsive tothe pulse generation signal 130. This laser drive current 124 isinjected to the laser 110, thereby driving the laser 110. In accordancewith a predetermined write pulse waveform, the laser 110 radiates thelaser beam 123. In this manner, the power level of the laser beam 123changes in accordance with the “write pulse waveform”.

The laser beam 123 emitted from the laser 110 passes the collimator lens109, half mirror 108 and objective lens 116 and is condensed onto theoptical disk 117. The condensed pulsed laser beam 123 locally heats aportion of the phase change recording layer of the optical disk 117 thatis spinning at a high velocity, thereby making marks and spaces alongthe track on the optical disk 117. In this case, if the phase changerecording layer is irradiated with the pulsed laser beam 123 at shortintervals, then the melted portions of the phase change recording layerwill combine together to form a single long mark. The power level of thelaser beam 123 depends on the write pulse waveform as described above.For that reason, if the write pulse waveform is controlledappropriately, a single long mark can be made by applying a plurality ofpulses.

In reading data from the optical disk 117, the rows of marks on theoptical disk 117 are scanned with the laser beam 123 with a power levelthat is low enough to avoid destroying (i.e., melting) the marks on thephase change recording layer. The light that has been reflected from theoptical disk 117 passes the objective lens 116 and half mirror 108 andthen enters the detector lens 106.

The laser beam that has been reflected from the optical disk 117 passesthe detector lens 106 and then is condensed on the photodetector 100.According to the light intensity distribution of the laser beam on thephotosensitive plane, the photodetector 100 converts the incoming lightinto an electrical signal. This electrical signal is amplified by thepre-amplifier 101 provided for the photodetector 100, thereby generatingthe read signal 120 that indicates whether or not there is a mark at thescan point on the optical disk 117.

The read signal 120 is subjected by the equalizer 103 to a waveformequalization process and then converted by the digitizer 104 into thedigital read signal 121. The decoder 105 converts this digital readsignal 121 in the opposite way to the data modulator 113, therebygenerating the read data 122.

The optical disk 117 may be either a single-layer disk that has only oneinformation storage layer or a double-layer disk that has twoinformation storage layers. Also, the optical disk 117 may be either arewritable optical disk that uses a phase change recording material or awrite-once optical disk that allows the user to write data there onlyonce.

The coding method does not have to be the (1, 7) modulation but may alsobe a 17 PP modulation or an 8-16 modulation. The 8-16 modulation has theshortest code length of 3 T. In that case, an extra code length of onemay be added to this preferred embodiment that uses the (1, 7)modulation.

Next, an exemplary configuration for the write processing system shownin FIG. 1 will be described in further detail with reference to FIG. 2.

The write data 127 is converted by the data modulator 113 into the writecode sequence 126 representing mark lengths, space lengths, andinformation about their top positions. The write code sequence 126 istransmitted to a mark length classifier 201 and a write pulse waveformtable 202. The mark length classifier 201 classifies the mark lengths ofthe write code sequence 126 following a predetermined rule and inputsthe results as a mark length classification signal 204 to the writepulse waveform table 202.

The counter 200 refers to the write code sequence 126 and measures thelength of time from a mark top position responsive to the referenceclock signal 128, thereby generating a count signal 205. In accordancewith the write code sequence 126, mark length classification signal 204and count signal 205, the write pulse waveform table 202 outputs thelevel producing signal 125, reflecting a predetermined write pulsewaveform, to the pulse shifter 115.

The pulsed waveform of the level producing signal 125 is compensated foron the time axis according to the write compensation table value of thewrite compensator 118 and then sent out as the pulse generation signal130 to the laser driver 111. The pulse generation signal 130 includes aPc generation signal 206, a Pb generation signal 207, a Pe generationsignal 208 and a Pw generation signal 209 that represents a power leveldefining the write pulse waveform. Responsive to the pulse generationsignal 130, the laser driver 111 drives the laser 110.

Next, the write code sequence of this preferred embodiment will bedescribed with reference to portions (a) through (h) of FIG. 3. In somecases, the length or level of a portion of the write pulse waveformneeds to be finely adjusted (i.e., write compensation needs to becarried out) in a certain period for some reason by reference to thepreceding and succeeding write patterns and code lengths. In thefollowing description of the write pulse waveform, when such writecompensation is carried out, the write pulse waveform is supposed to becompared to the original write pulse waveform yet to be finely adjusted.For that reason, the write pulse waveform will be described on thesupposition that the write pattern remains the same over a rather longdistance before and after the mark to be made. As used herein, the“rather long distance” means a distance that is much longer than thedistance on a medium to be affected by the application of the writeenergy for a period of time approximately corresponding to the detectionwindow width.

Portion (a) of FIG. 3 shows the reference clock signal 128 that is usedas a time reference for a write operation. Tw denotes one clock period.

Portion (b) of FIG. 3 shows the write code sequence 126 obtained bygetting the write data subjected to the NRZI conversion by the datamodulator 113. The signal waveform representing the write code sequence126 changes between level “1” and level “0”. The detection window widthis equal to Tw, which is the minimum unit of variation in the mark orspace length in the write code sequence 126.

Portion (c) of FIG. 3 schematically illustrates the planar shapes ofmarks and spaces to be actually recorded on the optical disk. The beamspot of the laser beam, which is incident on the optical disk to writedata thereon, shifts from the left to the right in portion (c) of FIG. 3while varying its power level, thereby leaving a series of marks shownin portion (c) of FIG. 3. The mark 301 shown in portion (c) of FIG. 3 ismade so as to represent level “1” in the write code sequence 126. Thelength of the mark 301 is proportional to that of the period that haslevel “1” in the write code sequence 126.

Portion (d) of FIG. 3 shows the count signal 205, in which the amount oftime that has passed since the top of the mark 301 or space 302 ismeasured on a Tw basis.

Portion (e) of FIG. 3 shows a mark length classification signal 307 in aconventional apparatus for the purpose of comparison. In thisconventional apparatus, the mark lengths are classified intoodd-number-of-times longer ones and even-number-of-times longer ones.

Portion (f) of FIG. 3 shows a write pulse waveform 303 in theconventional apparatus, which is the counterpart of the write codesequence 126 shown in portion (b) of FIG. 3. The write pulse waveform303 is generated by reference to the count signal 205, write codesequence 126 and mark length classification signal 307.

Portion (g) of FIG. 3 shows the mark length classification signal 204 ofthis preferred embodiment. In this preferred embodiment, the marklengths are classified into the shortest code length of 2 T, the secondshortest code length of 3 T, the third shortest code length of 4 T, andthe fourth shortest or less short code lengths, which are furtherclassified into odd-number-of-times longer code lengths andeven-number-of-times longer code lengths.

Portion (h) of FIG. 3 shows the write pulse waveform 304 of thispreferred embodiment corresponding to the write code sequence 126 shownin portion (b) of FIG. 3. This write pulse waveform 304 is generated byreference to the count signal 205, write code sequence 126 and marklength classification signal 204. The shortest cooling time of thiswrite pulse waveform 304 is about 1 Tw.

Hereinafter, signal waveforms for making marks according to the presentinvention will be described in detail with reference to FIG. 2 andportions (a) through (j) of FIG. 4. Portions (a) through (j) of FIG. 4show write pulse waveforms 400 through 407, respectively.

In this preferred embodiment, the data modulator 113 (see FIG. 2) adoptsa coding method in which the (1, 7) code modulation is followed by theNRZI modulation, each and every mark or space length falls within therange of 2 Tw to 8 Tw. This coding method is also applicable to even asituation where a signal of 9 Tw, for example, is intentionally insertedas a sync signal. However, this does not amend the coding rule of thedata modulator 113. Rather, the present invention is applicable for usein the data modulator 113 that complies with any arbitrary coding rule(e.g., 8-16 modulation).

First, the mark length classifier 201 of this preferred embodimentclassifies the code lengths n of the marks to be made into the fourgroups of 2 T, 3 T, 4 T and 5 T or more. If the code length n is 5 T ormore, the mark length classifier 201 divides (n−1) by the divisor of two(i.e., performs a remainder calculation), thereby obtaining a quotient.Then, the mark length classifier 201 outputs this quotient as a marklength classification signal. For example, if the code length n is five,then (5−1)=4 and four divided by the divisor of two is two, which is thequotient obtained. Meanwhile, if the code length n is six, then (6−1)=5and five divided by the divisor of two is also two, which means the samequotient is obtained. That is why the same mark length classificationsignal is output for a mark with 5 Tw length and a mark with a 6 Twlength.

By using such a mark length classification signal, the marks and spacesof the write code sequence can be classified into ones that areeven-number-of-times as long as the detection window width Tw and onesthat are odd-number-of-times as long as the detection window width Tw.In this preferred embodiment, the divisor is supposed to be two for thesake of simplicity. However, three or any other greater divisor may beused instead. Also, the mark length classifier 201 of this preferredembodiment operates so as to perform a remainder calculation. However,the present invention is in no way limited to this specific preferredembodiment.

Portions (a) through (j) of FIG. 4 will be referred to next.

Portion (a) of FIG. 4 shows the waveform of the reference clock signal128, while portion (b) of FIG. 4 shows the count signal 205 generated bythe counter 200. The amount of time that has passed since the top of amark is counted on a detection window width (Tw) basis. The time atwhich the count signal goes zero corresponds to the top of a mark orspace. Portions (c) through (j) of FIG. 4 show signal waveforms formaking marks with 2 Tw to 9 Tw lengths, respectively.

As used herein, the “mark making period” is defined as a period of timebetween the leading edge of the first pulse and the trailing edge of thelast pulse as shown in portion (j) of FIG. 4.

In making a mark with the 2 Tw length, the write pulse waveform duringthe mark making period consists of a single pulse with a length of 0.5Tw to 1 Tw and a level Pw as shown in portion (c) of FIG. 4.

In making a mark with the 3 Tw length, the write pulse waveform duringthe mark making period consists of a single pulse with a length of 1 Twor more but less than 2 Tw and with a level Pw as shown in portion (d)of FIG. 4. It should be noted that in this case, the mark making periodis supposed to be longer than that of the 2 Tw long one by at least 0.5Tw.

In making a mark with the 4 Tw length, the write pulse waveform duringthe mark making period consists of a single pulse with a length of 1.5Tw or more but less than 2.5 Tw and with a level Pw as shown in portion(e) of FIG. 4. It should be noted that in this case, the mark makingperiod is supposed to be longer than that of the 3 Tw long one by atleast 0.5 Tw.

In a conventional data recorder such as a DVD player/recorder, a markwith the 4 Tw length is made by using a write pulse waveform that hastwo write pulses Pw during a single mark making period as shown in FIG.13( a). As for DVDs, the write pulses have a wavelength of about 650 nm.In such an apparatus, if one tries to make a 4 Tw long mark using asingle write pulse Pw such as that shown in FIG. 13( b), then the markwidth broadens at the end portion as shown in FIG. 13( c). In contrast,according to this preferred embodiment, even by using a single writepulse such as that shown in FIG. 13( b), a mark of an appropriate shapecan be made with good reproducibility as shown in FIG. 13( d).

A Blu-ray Disc (BD) is now being developed as a next-generation opticaldisk. In a BD, the laser beam for reading and writing has a wavelengthof about 400 nm. Also, the material and composition of the storage layerof a BD are different from those of the storage layer of a DVD. Besides,BD and DVD have a lot of other differences in their physical structures.In a BD, the width and interval of the write pulses need to be narrowerthan those of a DVD. For that reason, if the data transfer rateincreases, a 4 Tw long mark may have a deformed shape even when writepulses having the waveform shown in FIG. 13( a) are used. On the otherhand, if a 4 Tw long mark is made by using a single write pulse such asthat shown in FIG. 13( b), a mark of a preferred shape can also beobtained even in a BD.

In making a mark with the 5 Tw length, the write pulse waveform duringthe mark making period includes a pulse with a length of 1 TTw and alevel Pw, which is followed by a period with a length of 1 Tw and alevel Pe and then a period with a length of 1 Tw and a level Pw as shownin portion (f) of FIG. 4.

In making a mark with the 6 Tw length, the write pulse waveform duringthe mark making period includes a pulse with a length of 1 TTw and alevel Pw, which is followed by a period with a length of 2 Tw and alevel Pe and then a period with a length of 1 Tw and a level Pw as shownin portion (g) of FIG. 4.

In making a mark with the 7 Tw length and a mark with the 9 Tw length(i.e., odd-number-of-times longer marks with code lengths over 5 Tw anda detection window width Tw), the write pulse waveform during the markmaking period includes an additional period with a length of 1 Tw and alevel Pe and another additional period with a length of 1 Tw and a levelPw per mark length of 2 Tw at the center of the mark making period asshown in portions (h) and (j) of FIG. 4.

In making a mark with the 8 Tw length (i.e., an even-number-of-timeslonger mark with a code length more than 5 Tw and a detection windowwidth Tw), the write pulse waveform during the mark making periodincludes an additional period with a length of 1 Tw and a level Pe andanother additional period with a length of 1 Tw and a level Pw per marklength of 2 Tw at the center of the mark making period as shown inportion (i) of FIG. 4. Thus, in a situation where

In a non-mark-making period, the level of the signal waveform ismaintained at Pe until the next mark making period irrespective of thespace length. In this preferred embodiment, the shortest Pe level period(i.e., the shortest cooling period) during the mark making period 305has a length of 1 Tw.

According to this preferred embodiment that adopts such a writestrategy, a mark of an appropriate shape can be made with goodreproducibility without being affected by the rising or falling rate ofthe optical output of a semiconductor laser diode. For example, if thedata transfer rate is 72 Mbps, then Tw becomes 7.6 ns. In this case, 0.5Tw=3.8 ns. Accordingly, if the rising and falling rates of the opticaloutput of the semiconductor laser diode are about 2 ns, neither the peakpower level nor the bottom power level can be reached and no mark of adesired shape can be obtained. Meanwhile, by adopting the write strategyof this preferred embodiment, the laser power can be modulated just asrepresented by the write pulse waveform even without increasing thecurrent rising and falling rates of the optical output of thesemiconductor laser diode.

Also, in this preferred embodiment, as to two codes, which have codelengths m and m+1, respectively, and to which a write pulse waveformwith the same number of write pulses Pw is assigned in the recordingmark making period, the write pulse waveforms are determined so as tosatisfy the inequality: (write pulse width of code length m)≦(writepulse width of code length m+1), where the “write pulse width of codelength m” is the width of an arbitrary Kth write pulse period includedin the period in which a recording mark with the code length m is madeand the “write pulse width of code length m+1” is the width of anarbitrary Kth write pulse period included in the period in which arecording mark with the code length m+1 is made.

As a result, the marks can be made in even more appropriate shapes.

Furthermore, in this preferred embodiment, in a period in which arecording mark corresponding to a code with a code length x of (n+3) ormore is made, a portion of the write pulse waveform with the erasurepower level Pe has a length of at least 1 Tw. In that case, even if theoptical output of the semiconductor laser diode has a rising or fallingrate of about 2 ns, the laser power can be modulated with a desiredwrite power. As a result, marks can be made with good reproducibility.

Embodiment 2

Hereinafter, a data recording method according to a second preferredembodiment of the present invention will be described with reference toFIG. 6.

The data recording method of this preferred embodiment can be carriedout just by modifying the operation program for the data recorder of thefirst preferred embodiment described above. That is why the datarecorder for use in this preferred embodiment has substantially the sameconfiguration as the counterpart shown in FIGS. 1 and 2, and detaileddescription thereof will be omitted herein.

The write pulse waveforms 600 through 607 of this preferred embodimentwill be described with reference to portions (a) through (j) of FIG. 6.

As can be seen easily by comparing portions (a) through (j) of FIG. 6 tothe counterparts of FIG. 4, the signal waveforms 600 through 607 adoptedin this preferred embodiment are similar to the signal waveforms 400through 407 shown in FIG. 4. Among other things, the signal waveforms600 through 602 are identical with the signal waveforms 400 through 402,respectively, as shown in portions (c) through (e) of FIG. 6. Thedifference between the first and second preferred embodiments lies inthe shapes of signal waveforms with code lengths n exceeding 5 Tw.

Referring to portion (f) of FIG. 6, in making a mark with the 5 Twlength, the write pulse waveform includes a pulse with a length of 1 TTwand a level Pw, which is followed by a period with a length of 1 Tw anda level Pb and then a period with a length of 1 Tw and a level Pw. Inthis case, it should be noted that the level Pb in the period interposedbetween the two pulses is lower than the level Pe.

In making a mark with the 6 Tw length, the write pulse waveform includesa pulse with a length of 1 Tw and a level Pw, which is followed by aperiod with a length of 2 Tw and a level Pb and then a period with alength of 1 Tw and a level Pw as shown in portion (g) of FIG. 6.

In making odd-number-of-times longer marks with code lengths over 5 Twand a detection window width Tw, the write pulse waveform includes anadditional period with a length of 1 Tw and a level Pb and anotheradditional period with a length of 1 Tw and a level Pw per mark lengthof 2 Tw at the center of the mark making period as shown in portions (h)and (j) of FIG. 6.

In making an even-number-of-times longer mark with a code length over 5Tw and a detection window width Tw, the write pulse waveform includes anadditional period with a length of 1 Tw and a level Pb and anotheradditional period with a length of 1 Tw and a level Pw per mark lengthof 2 Tw at the center of the mark making period as shown in portion (i)of FIG. 6.

According to this preferred embodiment, as to two codes, which have codelengths m and m+1 (where m is an integer equal to or greater than one),respectively, and to which a write pulse waveform with the same numberof write pulses Pw and the same number of periods with a bottom powerlevel Pb between two write pulses Pw is assigned in a recording markmaking period, the write pulse waveforms are determined so as to satisfythe inequality: (pulse width of code length m)≦(pulse width of codelength m+1), where the “pulse width of code length m” is the width of anarbitrary Kth period with the bottom power level Pb included in theperiod in which a recording mark with the code length m is made and the“pulse width of code length m+1” is the width of an arbitrary Kth periodwith the bottom power level Pb included in the period in which arecording mark with the code length m+1 is made. The shorter the codelength, the more easily the heat is accumulated in the end portion of amark. However, by satisfying the inequality (pulse width of code lengthm)≦(pulse width of code length m+1), the accumulation of heat can bereduced and the mark shapes can be adjusted.

Furthermore, in this preferred embodiment, in each recording mark makingperiod, a portion of the write pulse waveform with the bottom powerlevel Pb has a length of at least 1 Tw. In that case, even if theoptical output of the semiconductor laser diode has a rising or fallingrate of about 2 ns, the laser power can be modulated with a desiredwrite power. As a result, marks can be made with good reproducibility.

Embodiment 3

Hereinafter, a data recording method according to a third preferredembodiment of the present invention will be described with reference toFIG. 7.

The data recording method of this preferred embodiment can be carriedout just by modifying the operation program for the data recorder of thefirst preferred embodiment described above. That is why the datarecorder for use in this preferred embodiment has substantially the sameconfiguration as the counterpart shown in FIGS. 1 and 2, and detaileddescription thereof will be omitted herein.

The write pulse waveforms 700 through 707 of this preferred embodimentwill be described with reference to portions (a) through (j) of FIG. 7.

As can be seen easily by comparing portions (a) through (j) of FIG. 7 tothe counterparts of FIG. 6, the signal waveforms 700 through 707 adoptedin this preferred embodiment are similar to the signal waveforms 600through 607 shown in FIG. 6. The difference between the second and thirdpreferred embodiments is that a non-mark-making period begins with aperiod with a length of 1 Tw to 1.5 Tw and a level Pc and then the Pelevel is maintained until the next mark making period. In this preferredembodiment, these levels Pc and Pb are supposed to be two differentpower levels. Alternatively, the levels Pc and Pb may be set equal toeach other.

Embodiment 4

Hereinafter, a data recording method according to a fourth preferredembodiment of the present invention will be described with reference toFIG. 11.

The data recording method of this preferred embodiment can be carriedout just by modifying the operation program for the data recorder of thefirst preferred embodiment described above. That is why the datarecorder for use in this preferred embodiment has substantially the sameconfiguration as the counterpart shown in FIGS. 1 and 2, and detaileddescription thereof will be omitted herein.

The write pulse waveforms 1100 through 1107 of this preferred embodimentwill be described with reference to portions (a) through (j) of FIG. 11.

As can be seen easily by comparing portions (c) through (j) of FIG. 11to the counterparts of FIG. 4, the signal waveforms 1100, 1101 and 1103through 1107 adopted in this preferred embodiment are identical with thesignal waveforms 400, 401 and 403 through 407 shown in FIG. 4. Thispreferred embodiment is characterized in that in making a mark with the4 Tw length, the write pulse waveform includes a pulse with a length of0.5 Tw and a level Pw, which is followed by a period with a length of 1Tw and a level Pe and then a period with a length of 0.5 Tw and a levelPw as shown in portion (e) of FIG. 11. After that, the level Pe ismaintained until the next mark making period.

Portion (b1) of FIG. 11 shows a count signal 205 generated by thecounter 200 to measure the amount of time that has passed since the topof a mark on a detection window width (Tw) basis. The time at which thecount signal goes zero corresponds to the top of a mark or a space.

Portion (b2) of FIG. 11 shows a sub-count signal 210 generated by thecounter 200 and having a phase difference of 180 degrees with respect tothe reference signal. The time at which this count signal goes zero hasa phase lag of 180 degrees with respect to the top of a mark or a space.

As shown in portion (e) of FIG. 11, Pw has a pulse width of 0.5 Tw.However, this width may be any value that is equal to or greater than0.5 Tw. In this case, either or both of the leading and trailing edgesof each pulse are synchronous with the sub-count signal.

In this preferred embodiment, the trailing edge of the first pulse andthe leading edge of the second pulse in the signal waveform 1102 withthe 4 Tw length are synchronous with the sub-count signal 210.

Embodiment 5

Hereinafter, a data recording method according to a fifth preferredembodiment of the present invention will be described with reference toFIG. 12.

The data recording method of this preferred embodiment can be carriedout just by modifying the operation program for the data recorder of thefirst preferred embodiment described above. That is why the datarecorder for use in this preferred embodiment has substantially the sameconfiguration as the counterpart shown in FIGS. 1 and 2, and detaileddescription thereof will be omitted herein.

The write pulse waveforms 1200 through 1207 of this preferred embodimentwill be described with reference to portions (a) through (j) of FIG. 12.

Portion (a) of FIG. 12 shows the waveform of the reference clock signal128. Portion (b1) of FIG. 12 shows a count signal 205 generated by thecounter 200 to measure the amount of time that has passed since the topof a mark on a detection window width (Tw) basis. The time at which thecount signal goes zero corresponds to the top of a mark or a space.Portion (b2) of FIG. 12 shows a sub-count signal 210 generated by thecounter 200 and having a phase difference of 180 degrees with respect tothe reference signal. The time at which this count signal goes zero hasa phase lag of 180 degrees with respect to the top of a mark or a space.

In making a mark with the 2 Tw length, the write pulse waveform consistsof a pulse with a length of 1 Tw and a level Pw as shown in portion (c)of FIG. 12. The non-mark-making period begins with a period with alength of 1 Tw and a level Pc and then maintains a level Pe until thenext mark making period.

In making a mark with the 3 Tw length, the write pulse waveform consistsof a pulse with a length of 2 Tw and a level Pw as shown in portion (d)of FIG. 12. The non-mark-making period begins with a period with alength of 1 Tw and a level Pc and then maintains a level Pe until thenext mark making period. However, the mark making period is supposed tobe longer than that of the 2 Tw long one by at least 0.5 Tw.

In making a mark with the 4 Tw length, the write pulse waveform includesa pulse with a length of 1 Tw and a level Pw, which is followed by aperiod with a length of 1 Tw and a level Pb and then a period with alength of 1 Tw and a level Pw as shown in portion (e) of FIG. 12. Thenon-mark-making period begins with a period with a length of 1 Tw and alevel Pc and then maintains a level Pe until the next mark makingperiod.

In making even-number-of-times longer marks with a detection windowwidth Tw, the write pulse waveform includes an additional period with alength of 1 Tw and a level Pb and another additional period with alength of 1 Tw and a level Pw per mark length of 2 Tw at the center ofthe mark making period as shown in portions (g) and (i) of FIG. 12. Thenon-mark-making period begins with a period with a length of 1 Tw and alevel Pc and then maintains a level Pe until the next mark makingperiod.

In making a mark with the 5 Tw length, the write pulse waveform includesa pulse with a length of 1 Tw and a level Pw, which is followed by aperiod with a length of 2 Tw and a level Pb and then a period with alength of 1 Tw and a level Pw as shown in portion (f) of FIG. 12. Thenon-mark-making period begins with a period with a length of 1 Tw and alevel Pc and then maintains a level Pe until the next mark makingperiod.

In making a mark with the 7 Tw length, the write pulse waveform includesa pulse with a length of 1 Tw and a level Pw, which is followed by aperiod with a length of 1.5 Tw and a level Pb, a period with a length of1 Tw and a level Pw, and then a period with a length of 1.5 Tw and alevel Pb as shown in portion (h) of FIG. 12. The non-mark-making periodbegins with a period with a length of 1 Tw and a level Pc and thenmaintains a level Pe until the next mark making period.

In this case, either or both of the leading and trailing edges of theintermediate pulse is/are synchronous with the sub-count signal. In FIG.12, the leading and trailing edges of the second pulse are synchronouswith the sub-count signal.

After that, in making odd-number-of-times longer marks with a detectionwindow width Tw, a period with a length of 1 Tw and a level Pb andanother period with a length of 1 Tw and a level Pw are added per marklength of 2 Tw to the center of the mark making period as shown inportion (j) of FIG. 12. The non-mark-making period begins with a periodwith a length of 1 Tw and a level Pc and then maintains a level Pe untilthe next mark making period.

In some waveforms of this preferred embodiment, the level Pe is supposedto be the same as the level Pb or Pc. However, the level Pe may bedifferent from the level Pb or Pc.

Next, an example of adaptive mark compensation will be described withreference to the accompanying drawings. A high-density optical writeoperation sometimes causes write interference in which mark edges shiftdepending on the writing conditions. To prevent the write signal frombeing deteriorated by such interference, adaptive mark compensation maybe carried out.

The adaptive mark compensation means a compensation operation ofchanging the top incidence points or pulse widths of the laser beamaccording to the length of the given mark, i.e., whether the length ofthe mark is 2 T (2 Tm), 3 T (3 Tm ), 4T (4 Tm) or 5 T or more (≧˜5 Tm),as shown in FIG. 8.

FIG. 8 shows exemplary adaptive mark compensation in a situation wherethe write power is represented by binary values. By shifting dTtop andTtop with respect to the beginning of the mark and also shifting Tlp ordtlp with respect to the end of the recording mark according to the codelength of the recording mark among other parameters described above, theedge shifting at the beginning and end of the mark can be minimized andgood signal quality is realized.

FIG. 9 shows exemplary adaptive mark compensation in a situation wherethe write power is represented by four values. By shifting dTtop andTtop with respect to the beginning of the mark and also shifting dTewith respect to the end of the recording mark according to the codelength of the recording mark among other parameters described above, theedge shifting at the beginning and end of the mark can be minimized andgood signal quality is realized. Although the write power is supposed tobe represented by four values in this example, the same markcompensation is equally applicable to even a situation where threevalues are used by setting Pb=Pc.

The magnitude of shift that can be caused by the write compensation maybe defined by a very small step (of Tw/16, for example) with respect tothe reference clock signal using a delay line, for instance.

Also, the write compensation may be started either from a point in timeon the fundamental waveform responsive to the count signal or anotherpoint in time responsive to the sub-count signal.

In the fundamental waveform of this preferred embodiment, each pulsewidth and the widths of a period with the bottom power level and aperiod with the cooling power level in each mark making period aresupposed to be at least equal to 1 T. However, after the writecompensation has been done, each pulse for a mark of any of variouslengths preferably has a width of at least 0.5 Tw. In that case, thewriting conditions can be relaxed without being affected by the laserresponse speed so much.

COMPARATIVE EXAMPLE

Hereinafter, the patterns of write pulse waveforms 500 through 506 foran apparatus of a comparative example will be described with referenceto portions (a) through (j) of FIG. 5 and FIG. 10.

First, referring to FIG. 10, illustrated is a configuration for thewrite processing system of this apparatus.

The data modulator 1013 shown in FIG. 10 receives write data 1027 andconverts it into a write code sequence 1026. The mark length classifier1001 divides the code length n by the divisor of two (i.e., performs aremainder calculation) on the write code sequence 1025. This mark lengthclassifier 1001 classifies the marks and spaces of the write codesequence into ones of which the lengths are even numbers of times aslong as the detection window width Tw and ones of which the lengths areodd numbers of times as long as the detection window width Tw.

The counter 1000 measures the length of time from a mark top position ona detection window width Tw basis, thereby generating a count signal1005. Portion (b) of FIG. 5 shows the count signal 1005. The time atwhich the count signal 1005 goes zero corresponds to the top of a markor space.

A reference clock signal 1028 is input to the counter 1000 and the datamodulator 1013. The count signal 1005 is input to the write pulsewaveform table 1002, which outputs a level producing signal 1025 to thelaser driver 1011. In response, the laser driver 1011 outputs laserdrive current 1024.

Portion (c) of FIG. 5 shows a write pulse waveform while a mark with the2 Tw length is being made. The mark making period 305 includes a pulsewith a length of 1 Tw and a level Pw1. The non-mark-making period beginswith a period with a length of 1 Tw and a level Pb and then maintains alevel Pa until the next mark making period.

Portion (d) of FIG. 5 shows a write pulse waveform while a mark with the3 Tw length is being made. The mark making period 305 includes a pulsewith the same length of 1 Tw and the same level Pw1 as the counterpartshown in portion (c) of FIG. 5, which is followed by a period with alength of 1 Tw and a level Pw2. The non-mark-making period begins with aperiod with a length of 1 Tw and a level Pb and then maintains the levelPa until the next mark making period just like the write pulse waveformshown in portion (c) of FIG. 5. The non-mark-making period has the samewaveform in any of portions (e) and (f) of FIG. 5. That is to say,irrespective of the length of the space, every non-mark-making periodbegins with a period with a length of 1 Tw and a level Pb and thenmaintains the level Pa until the next mark making period. Thus, theshortest cooling period in the mark making period 305 has a length of 1Tw.

Portion (e) of FIG. 5 shows a write pulse waveform while a mark with the4 Tw length is being made. The mark making period 305 includes a pulsewith the same length of 1 Tw and the same level Pw1 as the counterpartshown in portion (c) of FIG. 5, which is followed by a period with alength of 1 Tw and a level Pa and then a period with a length of 1 Twand a level Pw3.

Portions (f) and (h) of FIG. 5 show write pulse waveforms in makingmarks with 5 Tw and 7 Tw lengths, respectively. Thus, in making a markof which the length is an odd number of times as long as the detectionwindow width Tw, a period with a length of 1 Tw and a level Pa andanother period with a length of 1 Tw and a level Pw3 are added per marklength of 2 Tw to the end of the mark making period. The non-mark-makingperiod always begins with a period with a length of 1 Tw and a level Pbirrespective of the space length and then maintains the level Pa untilthe next mark making period.

Portions (g) and (i) of FIG. 5 show write pulse waveforms in makingmarks with 6 Tw and 8 Tw lengths, respectively. Thus, in making a markof which the length is an even number of times as long as the detectionwindow width Tw, a period with a length of 1 Tw and a level Pa andanother period with a length of 1 Tw and a level Pw3 are added per marklength of 2 Tw to the end of the mark making period.

In this comparative example, the write power of the write pulse trainchanges stepwise, thus requiring a more complicated power control thanany preferred embodiment of the present invention. Also, in recording amark with a code length of 4 Tw, the semiconductor laser diode needs toemit radiation at a higher power level than the average power level atleast during a period with the 3 Tw length. When the storage density ofoptical disks rises in the near future to the point that very smallmarks need to be made, the radiation will have to be emitted for toolong a time in the comparative example. As a result, marks of a desiredshape will not be obtained.

INDUSTRIAL APPLICABILITY

According to the present invention, an apparatus for recording data on astorage medium by applying energy to the storage medium and making marksthat have a different physical property from the non-recorded portioncan make those marks quickly and accurately. As a result, the mark edgerecording technique, which will effectively contribute to increasing therecording linear density, can be adopted as the method of recording.

Consequently, the read/write operations can be done more quickly andwith more reliability, and yet the sizes of the apparatus for recordinginformation and the storage medium can be reduced as well. That is whythe present invention is very cost-effective.

1. A data recording method for recording data as edge positioninformation, including marks and spaces of multiple different lengths,on a storage medium by irradiating the storage medium with a pulsedenergy beam, the method comprising: (A) generating an NRZI data based onthe data to be recorded; (B) determining a write pulse waveform,defining the power modulation of the energy beam, according to the codelengths x of respective codes included in the NRZI data, the codelengths x (where x is an integer equal to or greater than one)corresponding to mark lengths of xTw (where Tw is a detection windowwidth); and (C) modulating the power of the energy beam based on thewrite pulse waveform, wherein if the shortest code length of the NRZIdata is n (where n is an integer equal to or greater than one), the step(B) includes assigning a write pulse waveform that has only one writepulse Pw to recording mark making periods corresponding to codes withcode lengths x of n, and n+1, and a write pulse waveform that hasmultiple write pulses Pw to recording mark making periods correspondingto codes with code lengths x of n+2 or more, respectively, wherein thewrite pulse waveform in the recording mark making period correspondingto codes with code lengths x of n+2 or more includes write pulses, ofwhich the number is equal to the quotient obtained by dividing x by two,and wherein the start position of a first pulse that is included in arecording mark making period of the write pulse waveform is shifted toadjust the start position of the first pulse, wherein the start positionof the first pulse is defined by a distance from a synchronizationposition of a reference clock that is used for forming the NRZI data,wherein the code lengths x are classified into at least four groups, andeach of four code lengths x of n, n+1, n+2 and n+3 belongs to differentone of the at least four groups, and wherein the width of the firstpulse and the shift of the start position of the first pulse areadjusted according to the at least four groups.
 2. A storage mediumcomprising a recording region for recording data as edge positioninformation, including marks and spaces of multiple different lengths,on a storage medium by being irradiated with a pulsed energy beam,wherein a power modulation of the energy beam is defined by a writepulse waveform, according to the code lengths of respective codesincluded in an NRZI data that is generated based on data to be recorded,the code lengths x (where x is an integer equal to or greater than one)corresponding to a mark length xTw (where Tw is a detection windowwidth); and wherein if the shortest code length of the NRZI data is n(where n is an integer equal to or greater than one), each write pulsewaveform for code lengths x of n and n+1 has only one write pulse, andeach write pulse waveform for code lengths x of n+2 or more has multiplewrite pulses, wherein the write pulse waveform in the recording markmaking period corresponding to codes with code lengths x of n+2 or moreincludes write pulses, of which the number is equal to the quotientobtained by dividing x by two, and wherein the start position of a firstpulse that is included in a recording mark making period of the writepulse waveform is shifted to adjust the start position of the firstpulse, wherein the start position of the first pulse is defined by adistance from a synchronization position of a reference clock that isused for forming the NRZI data, wherein the code lengths x areclassified into at least four groups, and each of four code lengths x ofn, n+1, n+2 and n+3 belongs to different one of the at least fourgroups, and wherein the width of the first pulse and the shift of thestart position of the first pulse are adjusted according to the at leastfour groups.
 3. A data reproduction method for reproducing data recordedon the storage medium according to claim 2, the method comprising:reproducing the data recorded on the recording region of the storagemedium by irradiating the storage medium with a light beam.